Method for producing bubble domains in magnetic film-substrate structures

ABSTRACT

A METHOD FOR PRODUCING A BUBVBLE COMAIN IN A MAGNETIC SINGLE CRYSTAL GARNET FILM-SUBSTRATE STRUCTURE IS DISCLOSED. THE METHOD INVOLVES THE EPITAXIAL DEPOSITION OF AN IRON GARNET FILM OF THE PROPER CRYSTALLOGRAPHIC ORIENTATION AND HAVING A NEGATIVE MAGNETOSTRICTION CONSTANT ON A GARNET SUBSTRATE IN WHICH THE ROOM TEMPERATURE LATTICE CONSTANT OF THE SUBSTRATE IS LARGER THAN THE ROOM TEMPERAURE LATTICE CONSTANT OF THE FILM, PREFERABLY BY AN AMOUNT LESS THAN 0.016 ANGSTROM.

April 17, 1973 J. E. MEE E AL 5 METHOD FOR PRODUCING BUBBLE DOMAINS INMAGNETIC FILM-SUBSTRATE STRUCTURES Filed Dec. 28, 1970 INVENTORS gm E.E5

United States Patent O 3,728,152 METHOD FOR PRODUCING BUBBLE DOMAINS INMAGNETIC FILM-SUBSTRATE STRUCTURES Jack E. Mee, Paul .I. Besser, GeorgeR. Pulliam, David M. Heinz, and Perry E. Elkins, Orange County, Calif.,assignors to North American Rockwell Corporation, El Segundo, Calif.

Filed Dec. 28, 1970, Ser. No. 101,786 Int. Cl. Hlllf 10/02 US. Cl.117235 5 Claims ABSTRACT OF THE DISCLOSURE A method for producing abubble domain in a magnetic single crystal garnet film-substratestructure is disclosed. The method involves the epitaxial deposition ofan iron garnet film of the proper crystallographic orientation andhaving a negative magnetostriction constant on a garnet substrate inwhich the room temperature lattice consant of the substrate is largerthan the room temperaure lattice constant of the film, preferably by anamount less than 0.016 angstrom.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to bubble domains and more particularly to a method of forming acraze-free film having bubble domains therein.

(2) Description of prior art Magnetic bubble domains in a sheet ofmagnetic medium, such as yttrium orthoferrite, are well known in the artand are described in US. Pat. No. 3,460,116 and others. Magnetic bubbledomains in composite structures having a thin film of a single crystaliron garnet on an oxide substrate are disclosed in the copending patentapplications to Mee et al., US. Ser. Nos. 16,446 and now US. Pat. No.3,645,788 and 16,447, filed Mar. 4, 1970. These copending patentapplications are incorporated herewith.

Some of the bubble domain composite single crystal film-substratestructures reported in the prior art have had crazing, that is cracking,of the film, making them unsuitable for certain types of bubble domaindevice applications. Other iron garnet film-substrate structures wereobserved to have domains whose magnetization directions are in the planeof the film in contrast to the desired bubble domains whosemagnetization directions are perpendicular to the plane of the film.

SUMMARY OF THE INVENTION It is a primary objectof this invention toprovide an improved method of forming a single crystal iron garnetfilm-substrate structure having bubble domains therein.

It is another object of this invention to provide a method of forming abubble domain film-substrate structure having a craze-free film surface.

These and other objects of this invention are accomplished by a methodin which the uniaxial anisotropy necessary for bubble domain formationin a craze-free film-substrate structure is affected by proper controlof the mechanical stress present in the film at room temperature. Aspecific step in the method involves depositing a single crystal irongarnet film of the proper crystallographic and having a negativemagnetostriction constant on a substrate in which the room temperaturelattice constant of the substrate is larger than the room temperaturelattice constant of the film preferably by an amount less han 0.016angstrom.

An example of a preferred embodiment in accordance With this inventionis to chemically vapor deposit a gal- 3,728,152 Patented Apr. 17, 1973BRIEF DESCRIPTION OF THE DRAWING The drawing shows a magnetic bubbledomain filmsubstrate structure made in accordance with the method ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION This invention involves a processin which a single crystal iron garnet material is chemically vapordeposited to form a film on a substrate. It is necessary that the singlecrystal material have the proper crystallographic orientation to takeadvantage of the negative magnetostriction. In addition the room latticeconstant of the substrate is larger than the room lattice constant ofthe deposited film, preferably by an amount less than 0.016 angstrom.The resultant film-substrate structure has a craze-free film with bubbledomains therein.

In general, the normal source of uniaxial anisotropy observed inmagnetic materials is the crystal structure of the material. [Whensingle crystal platelets with negative magnetostriction constants (li x0 are under stress, the magnetostriction contribution tends to make thenormal to the plane of the platelet an easy axis of magnetization if theplatelet is in tension (r.r and a hard axis if the platelet is incompression (a U))\ and h are the saturation values of the linearmagnetostriction constants along the l00 and 111 directions,respectively, and 0' is the stress in the plane of the material.

The room temperature magnetostriction constants of selected iron garnetare listed in the following table.

Magnetostrietion constant Iron garnet M00 (X10 X111 (X10 Some of theseiron garnet materials, for example Tb3FC5O 2 and Yb Fe O have both anegative and a positive magnetostriction constant. In the practice ofthis invention the crystallographic orientation of the garnet film mustbe chosen to take advantage of the negative magnetostriction constant.In the case with Tb Fe O material, the orientation would be With the YbFe O material, the orientation would be {111}.

The values of the magnetostriction constants of the iron garnetmaterial, as well as its magnetization, can be varied by depositing afilm containing a mixture of two or more pure iron garnets and/or bysubstituting other cations for iron ions.

It is understood that whether there is mixing and/or substitution ornot, the condition for bubble domain formation in the iron garnetmaterial, H /41rM 1, has to be satisfied, where H is the uniaxialanistotropy field and 41rM is the magnetization.

In magnetic oxide film-substrate structures formed by chemical vapordeposition, the dominant source of uni- A preferred substrate materialis mixed yttrium-gadolinium gallium garnet when the film material isgallium substituted yttrium iron garnet.

In accordance with this invention, an iron garnet film of the properorientation and having a negative magnetoaxial anistotropy 1s themagnetostrictive effect resulting striction constant is deposited on agarnet substrate in from the stress existing in the film. This stress isdue to which the room temperature lattice constant of the subthedifference between the lattice constants and the thermal Strate islarger than the room temperature lattiee Constant expansion coefficientsof the film and substrate and may of the Preferably y all amount lessthan -016 be in the form of t i o compression, angstrom. When thesubstrate lattice constant exceeds the This i venti ifi ll covers a th df f i film lattice constant, the film is in tension and bubble a bubbledomain structure by depositing a magnetic single domains are Presentthereih- The Preferred difierehees crystal garnet fil f th Proper i t tid h i a tween the lattice constants is of the order of 0.005 to negativemagnetrostriction constant on a substrate in 0-010 ahgstrom- When thelattiee constant difference is which th fil i i t i 0.016 angstrom ormore, the tension or stress is so great A eopending li i to M et 1 thatthere is crazing or cracking of the film. When the sub- 101,785, f l d D28, 1970, covers a h d of fo min strate lattice constant is smaller thanthe film lattice cona bubble domain structure by depositing a magneticsingle Staht by an amount less than about 0935 angstrom, the crystalgarnet film of the proper orientation and having film is in compressionand there are he b e d s a positive magnetostriction constant on asubstrate in shlee h normal to Plane of the film is the hardmaghetiZawhi h th fil i i compression tron axis and the domainmagnetizations lie in the plane.

A copending li ti to M l l S N 1011 7 As previously discussed, thedifference in the coefficients fil d D 23, 1970, covers a Second methodf f mi of thermal expansion between the film and the substrate abubbledomain structure by depositing amagnetic single contributes to the totalStress P in the The crystal garnet fil f the Propelerientafien andhaving thermal expansion stress contribution is within acceptable 3negative magnetostriction constant on a substrate in limits as long asthe coeflicient of thermal expansion of the hi h h fil i i i substrateis the same as or lower than that of the fih'n by As shown in thedrawing, an oxide substrate 10 is suban amount not more than X betWeellC- j t d ef ably to a chemical vapor deposition Step to and 1200 C. Acertain amount of mismatch between filmid a hi fil f magnetic bubbledomain material, substrate room temperature lattice constants and/or fil12, T deposition Step is carried out in accordance thermal expansioncharacteristics is required in order to i h h copending application,833,268 filed provide the stress which produces the uniaxial anisotropyJ 16 1969 and assigned to the assighees f the present necessary forbubble domain formation. If film and subinvention. This pending patentapplication is incorporat d strate are too closely matched in bothlattice constant and herewith by reference hereto. The film 12 may bedeposthemtal expaneloni h Proper Stress neeesaary for bubble ited bysputtering techniques or by a liquid phase epitaxial domam formatlonW111 not be achieved- PI'OCCSS. EXAMPLE I The substrate 10 ismonocrystalline garnet having a I Q O formulation wherein the Jconstituent of the A {111} gallium substltuted yttnum Iron garnet Waferformulation is at least one element selected from 40 the groupconsisting of cerium, praseodymium, neodymium, promethium, Samarium,europium, gadolinium, having a lattice constant of 12.357 angstroms wasdeterbium dysprosium, holmium, erbium, thulium, yetterposited 011 amixed yttrium-gadolinium gallium garnet, bium, lutetium, lanthanum,yttrium, calcium, bismuth; 2.7 0,a 5O by chemical vapor depositiontechniques. and the Q constituent of the wafer formulation is at leastThe lattieeeehstaht 0f the mixed yttrium-gadolinium one element selectedfrom the group consisting of indium, hum garnet Was Whieh eXeeeded t Ofthe fi m gallium, scandium, titanium, vanadium, chromium, by 0-010ahgstrom- The resultant Structure had a Crazemanganese, rhodium,zirconium, hafnium, niobium, tantar m W h had bu le d mains therein.lum, aluminum, phosphorous, arsenic and antimony. EXAMPLES Examples ofsubstrate materials are mixed yttriumgadolinium gallium garnet,gadolinium gallium garnet, Examples I-V are listed below in thefollowing able. aluminum substituted gadolinium gallium garnet, terbiumIn Example II, a gallium substituted yttrium iron garnet gallium garnet,and dysprosium gallium garnet. film was deposited in accordance withthis invention on The film of the bubble domain material is a single agadolinium gallium garnet in which the substrate lattice crystal garnetfilm having a J Q O formulation wherein constant exceeded the filmlattice constant at room temthe I constituent of the film formulationhas at least one perature by 0.019. This structure had bubble domains inelement selected from the group of cerium, praseodymium, the film andalso had crazing on the film surface making neodymium, promethium,samarium, gadolinium, terbium, it less useful for certain applications.Examples III, IV dysprosium, holmium, erbium, thulium, ytterbium,lutetiand V were the gallium substituted yttrium iron garnet um,lanthanum and yttrium; the Q constituent of the film films on differentsubstrates in which the film lattice conformulation is taken from thegroup consisting of iron, stant exceeded the substrate lattice constantby less than iron and aluminum, iron and gallium, iron and indium, 0.035angstrom. As a result, these films were in compresiron and scandium,iron and titanium, iron and vanadium, sion and there were no bubbledomains, only domains iron and chromium, and iron and manganese. whosemagnetization lies inthe plane.

TABLE Film Subtrate Substrate lattice constant- In-Plane Grazing ExampleLattice con- Lattice confilm lattice Bubble vector on film No. Materialb stant, A. Substrate material stem, A. constant, A. domain domainssurface Stress I YaGai-zFea-sOm 12.357 Gdz-7Y Ga5O1z Yes N0 None.Tension II.-- YsGarzFea-aom 12.357 GdsGasOm III mom-tremors 12.357GdeAlwGar-lon Compresslon; IV" YaGar-zFea'aou 12.357 TbgGason D0- VYaGai-zFea-soia 12.357 Dy Ga Oiz D0- 5 At room temperature.

b 111 orientation, negative magnetostriction constant: e 111orientation.

What is claimed is:

1. A methodof producing a bubble domain containing single crystal irongarnet film-substrate structure comprising the step of depositing aniron garnet film of the proper crystallographic orientation and having anegative magnetostriction constant on a substrate in which the substratehas a room temperature lattice constant which exceeds the roomtemperature lattice constant of the iron garnet film, by an amount lessthan .016 angstrom.

2. A method as described in claim 1 whereby the room temperature latticeconstant oft he substrate exceeds the room temperature lattice constantof the film by an amount between 0.005 and 0.010 angstrom.

3. A method as described in claim 1 whereby said film is deposited by achemical vapor deposition technique.

4. A method of producing a bubble domain containing film-substratestructure comprising the steps of depositing a yttrium iron garnet filmof the proper crystallographic orientation and having a negativemagnetostriction constant on a substrate in Which the substrate has aroom temperature lattice constant which exceeds the room temperaturelattice constant of said film by an amount less than 0.016 angstrom.

5. A method as described in claim 4 whereby said substrate is a mixedyttrium-gadolinium gallium garnet.

References Cited UNITED STATES PATENTS 3,525,638 8/1970 Archey 117107.1X 3,486,937 12/1969 Linares 117235 X 3,429,740 2/1969 Mee 117-235 X3,131,082 4/1964 Gambino 117-235 3,573,099 3/1971 Moore et a1 117235 X3,645,787 2/ 1972 Mee et all. 117--239 3,645,788 2/1972 Mee et a1.117-235 3,617,381 11/1971 Hanak 117235 OTHER REFERENCES Giess et aL: IBMTech. Dis. BulL, p. 517, 117-235, vol. 13, N0. 2, July 1970.

WILLIAM D. MARTIN, Primary Examiner Bv D. PIANALTO, Assistant ExaminerUS. Cl. X.R. 117-106 R V UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,728,152 Dated April 17', 1973 It is certifiedthat error appears in the above-identified. patent and that said LettersPatent are hereby corrected as shown below:

.lolrmn 2, line 1.;2, v "garnet should read garnets Column 3, line 22,"101.787 should read 101,787

Column 5', claim 2, line 11, "oft he" should read Signed and sealed this21st day of May 1971+.

(SEAL) Attest:

EDWARD I -LFLETCZEJR, J R. C MAR HALL DAHN Attesting OfficerCommissioner of Patents USCOMM-DC 60376-P69 wu.s. eovznunzm' PRINTINGomc: is o-su-su,

FORM PO-105O (IO-69)

